This invention relates to fire-retardant latices which are useful as binders for manufacturing non-woven fabrics. The fire-retardant latex binders of this invention are particularly useful in manufacturing non-woven fiberglass furnace filters.
Various latex compositions can be used as binders for non-woven fabrics. In many applications, it is desirable for the latex binder composition to provide fire-retardant characteristics. For instance, in clothing and household applications, it is normally desirable for the latex employed to contain a fire-retardant material.
A wide variety of chemical agents can be used in latex binders as fire-retardants. For instance, tris-(2,3-dibromopropyl) phosphate was once widely used as a flame-retardant in manufacturing children""s sleepwear. However, tris-(2,3-dibromopropyl) phosphate is no longer used in such applications because testing has showed that it might be carcinogenic. Other flame-retardant compounds that have been developed to replace tris-(2,3-dibromopropyl) phosphate include tris(1,3-dichloroisopropyl) phosphate and a mixture of two cyclic phosphonate esters.
U.S. Pat. No. 2,036,854 discloses that a mixture of ammonium borate or phosphate with an ammonium halide, such as ammonium bromide, is useful for flame-proofing textile materials. U.S. Pat. No. 2,036,854 further reports that the ammonium halide appears to greatly enhance the flame-extinguishing properties of the ammonium borate or phosphate.
U.S. Pat. No. 2,452,054 discloses the use of diammonium phosphate and ammonium bromide as a flame-retardant for use on cellulosic materials. It is further disclosed in U.S. Pat. No. 3,061,492 that ammonium bromide can be used as a flame-retardant for unsaturated polyester resin compositions.
U.S. Pat. No. 3,840,488 discloses the use of ammonium bromide and urea as flame-retardant additives for styrene-butadiene rubber (SBR) latex that is used for textile treatment and carpet backing applications. However, U.S. Pat. No. 3,840,488 further discloses that the utilization of ammonium bromide and urea in such latices has the undesirable effect of reducing the viscosity of the latex. The teachings of U.S. Pat. No. 3,840,488 further indicate that this undesirable decrease in the viscosity of the latex can be prevented by the addition of a halo alkyl phosphoric acid or salt.
U.S. Pat. No. 5,484,839 discloses a flame-retardant natural or synthetic latex which is grafted with ring-halogenated, ethylenically unsaturated aromatic monomers. These grafted latex compositions are reported to be useful as non-woven filter media binders, as backcoatings for woven upholstery and draperies, and in other applications.
U.S. Pat. No. 4,239,670 appreciates the fact that the addition of some flame-retardant materials, such as diammonium phosphate, to latex can cause the latex to become unstable. U.S. Pat. No. 4,239,670 further notes that such instability can render the latex unsuitable for its intended purpose. U.S. Pat. No. 4,239,670 solves the problem of latex instability caused by the addition of diammonium phosphate by further adding one part by weight of ammonium bromide per part by weight of diammonium phosphate added to the latex.
It has been unexpectedly found that the stability of styrene-butadiene rubber latices containing diammonium phosphate can be significantly improved by adding from 0.1 phr (parts per 100 parts by weight of dry rubber) to 5 phr of a sulfonate surfactant and 0.1 phr to 4 phr of an ethylene oxide/propylene oxide/ethylene oxide triblock polymer nonionic surfactant thereto. By utilizing this technique fire-retardant latex binder compositions containing diammonium phosphate can be made without the need to add ammonium bromide to attain a satisfactory level of stability. Since diammonium phosphate can be included in the latex composition, it is not necessary to graft a ring-halogenated, ethylenically unsaturated aromatic monomer onto the latex composition to render it fire-retardant.
The present invention specifically discloses a fire-retardant latex binder composition which is comprised of (1) water, (2) a styrene-butadiene rubber, (3) a fatty acid soap, (4) a sulfonate surfactant, (5) an ethylene oxide/propylene oxide/ethylene oxide triblock polymer, wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer has a number average molecular weight of at least 8000, and (6) about 10 phr to about 50 phr of diammonium phosphate. This fire-retardant latex binder composition is particularly useful as a binder for manufacturing non-woven fabric.
The present invention further discloses a process for manufacturing a furnace filter which comprises (I) applying a fire-retardant latex binder composition to a fiberglass matrix to produce a latex-coated fiberglass matrix, wherein the fire-retardant latex binder composition is comprised of (1) water, (2) a styrene-butadiene rubber, (3) a fatty acid soap, (4) a sulfonate surfactant, (5) an ethylene oxide/propylene oxide/ethylene oxide triblock polymer, wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer has a number average molecular weight of at least 8000, and (6) about 10 phr to about 50 phr of diammonium phosphate, and (II) drying the latex coated fiberglass matrix to produce the furnace filter.
The fire-retardant latex binder compositions of this invention are made by simply mixing about 10 phr (parts per hundred parts by weight of rubber) to about 50 phr of diammonium phosphate into a styrene-butadiene latex that contains a fatty acid soap, a sulfonate surfactant and an ethylene oxide/propylene oxide/ethylene oxide triblock polymer, wherein the ethylene oxide/propylene oxide/ethylene oxide triblock polymer has a number average molecular weight of at least 8000. Such a latex is manufactured and sold by The Goodyear Tire and Rubber Company under the name Pliolite(copyright) 5000C. In most cases, from about 15 phr to about 40 phr of diammonium phosphate will be mixed into the latex.
Such styrene-butadiene rubbers in the latex is comprised of repeat units which are derived from styrene monomer and 1,3-butadiene rubber. Such styrene-butadiene rubbers will typically be comprised of repeat units which are derived from about 1 to about 40 weight percent styrene and about 60 to about 99 weight percent butadiene. The styrene-butadiene rubber in the latex will typically contain from about 10 weight percent to about 30 styrene and from about 70 weight percent to about 90 weight percent butadiene. The styrene-butadiene rubber in the latex will more preferably contain about 15 weight percent to about 25 weight percent styrene and from about 75 weight percent to about 85 weight percent butadiene.
The styrene-butadiene rubber latex can be synthesized using a fatty acid soap system and conventional emulsion polymerization techniques. Such emulsion polymerizations generally utilize a charge composition which is comprised of water, styrene monomer, 1,3-butadiene monomer, an initiator and a fatty acid soap. Such polymerizations can be conducted over a very wide temperature range from about 0xc2x0 C. to as high as about 100xc2x0 C. Such emulsion polymerizations are typically conducted at a temperature which is within the range of about 5xc2x0 C. to about 60xc2x0 C.
The fatty acid soap used in such polymerizations may be charged at the outset of the polymerization or may be added incrementally or proportionately as the reaction proceeds. Normally, from about 2 phm (parts by weight per 100 parts by weight of monomer) to about 7 phm of the fatty acid soap will be charged into the polymerization medium. It is typically preferred for the polymerization medium to contain from about 4 phm to about 6 phm of the fatty acid soap.
The emulsion polymerizations used in synthesizing the styrene-butadiene rubber latex may be initiated using free radical catalysts, ultraviolet light or radiation. To insure a satisfactory polymerization rate, uniformity and a controllable polymerization, free radical initiators are virtually always used to initiate such emulsion polymerizations. Free radical initiators which are commonly used include the various peroxygen compounds such as potassium persulfate, ammonium persulfate, benzoyl peroxide, hydrogen peroxide, di-t-butylperoxide, dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, decanoyl peroxide, lauroyl peroxide, cumene hydroperoxide, p-menthane hydroperoxide, t-butylhydroperoxide, acetyl acetone peroxide, methyl ethyl ketone peroxide, succinic acid peroxide, dicetyl peroxydicarbonate, t-butyl peroxyacetate, t-butyl peroxymaleic acid, t-butyl peroxybenzoate, t-butyl peroxymaleic acid, t-butyl peroxybenzoate, acetyl cyclohexyl sulfonyl peroxide, and the like; the various azo compounds such as 2-t-butylazo-2-cyanopropane, dimethyl azodiisobutyrate, azodiisobutyronitrile, 2-t-butylazo-1-cyanocyclohexane, 1-t-amylazo-1-cyanocyclohexane, and the like; the various alkyl perketals, such as 2,2-bis-(t-butylperoxy)butane, ethyl 3,3-bis(t-butylperoxy)butyrate, 1,1-di-(t-butylperoxy)cyclohexane, and the like.
The emulsion polymerization system used in the synthesis of the latex can be treated at the desired degree of conversion with shortstopping agents, such as hydroquinone or a combination of the sodium salt of N,N-dimethyl dithiocarbamate with N,N-diethyl hydroxylamine. Typical stabilizing agents and standard antioxidants can also be added to the latex.
In accordance with this invention, from about 0.1 phr to 5 phr of a sulfonate surfactant and from about 0.1 phr to about 4 phr of an ethylene oxide/propylene oxide/ethylene oxide block terpolymer will be added latex. It is typically preferred to add 1 phr to 3 phr of the sulfonate surfactant and 0.4 phr to 2 phr of the ethylene oxide/propylene oxide/ethylene oxide block terpolymer to the styrene-butadiene latex. It is typically more preferred to add 1.5 phr to 2.5 phr of the sulfonate surfactant and 0.8 phr to 1.2 phr of the ethylene oxide/propylene oxide/ethylene oxide block terpolymer to the styrene-butadiene latex.
Some representative examples of sulfonate surfactants that can be employed include: alkane sulfonates, esters and salts (such as alkylchlorosulfonates) and alkylsulfonates with the general formula:
RSO3H 
wherein R is an alkyl group having from 1 to 20 carbon atoms; sulfonates with intermediate linkages such as ester and ester-linked sulfonates such as those having the formula:
RCOOC2H4SO3H 
and
ROOCxe2x80x94CH2xe2x80x94SO3H 
wherein R is an alkyl group having from 1 to 20 carbon atoms such as dialkyl sulfosuccinates; ester salts with the general formula: 
wherein R is an alkyl group having from 1 to 20 carbon atoms, alkarylsulfonates in which the alkyl groups contain preferably from 10 to 20 carbon atoms (e.g., dodecylbenzenesulfonates, such as sodium dodecylbenzenesulfonate) and alkyl phenol sulfonates.
Disulfonated surfactants having the structural formula: 
wherein R represents a linear or branched alkyl group containing from about 6 to about 16 carbon atoms and wherein X represents a metal ion, such as a sodium ion, have proven to be excellent surfactants for making the latex used in the practice of this invention. Such surfactants are sold by The Dow Chemical Company as Dowfax(trademark) anionic surfactants.
The ethylene oxide/propylene oxide/ethylene oxide triblock polymers that can be used are of the structural formula: 
These triblock polymers will typically have a number average molecular weight of at least 8000. The triblock polymer will typically have a number average molecular weight which is within the range of about 10,000 to about 20,000. It is normally preferred for the triblock polymer to have a number average molecular weight which is within the range of 10,500 to 16,000. It is typically more preferred for the triblock polymer to have a number average molecular weight which is within the range of 11,000 to 14,000.
The polyoxypropylene block in the triblock polymer will typically have a number average molecular weight which is within the range of about 2,000 to about 12,000 and will more typically have a number average molecular weight which is within the range of 2,500 to 8,000. The polyoxypropylene block in the triblock polymer will preferably have a number average molecular weight which is within the range of 3,000 to 6,000. The polyoxypropylene block in the triblock polymer will more preferably have a number average molecular weight which is within the range of 3,500 to 4,500.
The polyoxyethylene blocks in the triblock polymer will typically comprise 50 weight percent to 90 weight percent of the total weight of the triblock polymer (the polyoxypropylene blocks will, of course, comprise the remaining 10 weight percent to 50 weight percent of the triblock polymer). The polyoxyethylene blocks in the triblock polymer will preferably comprise 60 weight percent to 80 weight percent of the total weight of the triblock polymer with the polyoxypropylene blocks comprising the remaining 20 weight percent to 40 weight percent of the triblock polymer. The polyoxyethylene blocks in the triblock polymer will preferably comprise 70 weight percent to 75 weight percent of the total weight of the triblock polymer with the polyoxypropylene blocks comprising the remaining 25 weight percent to 30 weight percent of the triblock polymer. It is preferred for the triblock polymer to have a HLB (hydrophilic/lipophilic balance) number which is within the range of about 18 to about 26. It is more preferred for the triblock polymer to have a HLB number which is within the range of 18 to 23. Pluronic(copyright) F108 surfactant and Pluronic(copyright) F127F surfactant are representative examples of ethylene oxide/propylene oxide/ethylene oxide triblock polymers that can be used in making the fire-retardant latex binder compositions of this invention.
The fire-retardant latex binder compositions of this invention can be employed as a binder for manufacturing a wide variety of non-woven fabrics. For example, non-woven fabrics can be manufactured using the fire retardant latex binder formulations of this invention using cotton fibers, polyester fibers, rayon fibers, nylon fibers, cellulosic fibers, fiber glass or various mixtures of such fibers. The fire retardant latex binders of this invention are particularly useful in manufacturing fiber glass furnace filters.
The fire-retardant latex binder compositions of this invention can be applied to substrates in manufacturing non-woven fabrics using any method known in the art. For instance, the fire-retardant latex binder composition can be applied to unwoven substrate fibers by kiss rolling, knife coating, airless spray or padding. Irrespective of which method of application is used, the latex binder which has been applied to the fibers needs to be dried or cured. This drying step is normally conducted by heating the fibers at an elevated temperature for a short period of time which is sufficient to effect drying and a proper cure. The temperature used in the drying step will typically be within the range of about 80xc2x0 C. to about 160xc2x0 C. and will more typically be within the range of about 110xc2x0 C. to about 140xc2x0 C.
Fiberglass is typically used in manufacturing furnace filters since the fiber can experience high temperatures during periods of its normal service life. In manufacturing such furnace filters, the fire-retardant latex binder is normally sprayed onto a fiberglass matrix of the desired size and shape. The binder will be applied at a level which is sufficient to penetrate the fiberglass matrix. After the binder has been applied to the fiberglass matrix, the latex-coated matrix is dried using a conventional procedure. For instance, dry air can be circulated through the latex-coated fiberglass matrix at an elevated temperature which is within the range of about 100xc2x0 C. to about 150xc2x0 C.
This invention is illustrated by the following examples which are merely for the purpose of illustration and are not to be regarded as limiting the scope of the invention or the manner in which it can be practiced. Unless specifically indicated otherwise, parts and percentages are given by weight.